Carrier-wave signaling system



Jan. 8 1924.

C. WHITE CARRIER WAVE SIGNALING SYSTEM Filed Dec. 21 1920 lili llll.

Patented Jan. 8, 1924.

UNITED sra'rlzsv PATENT oFFlcE.

CHARLES WHITE, OF EAST ORANGE, NEW JERSEY, .ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., CORPORATION OF NEW YORK.

CARRIER-WAVE SIGNALING SYSTEM` Application led December 21, 1920. Serial Nc. 432,191.

To all whom it may cmwem;

Be it known that I, CHARLES WHITE, a citizen of the United States, residin at East Orange, in the county of Essex, tate of New Jersey, have invented certain new and useful Improvements in Carrier-Wave Signaling Systems, ofv which the following is a full, clear, concise, and exact description.

This invention relates to carrier wave signaling systems and more particularly to systems of multiplex telephony employing carrier waves wherein carrier waves of distinctive frequencies are used for transmissions in opposite directions, and wherein such carrier waves are normally impressed upon the transmission medium. Such medium may comprise any of the natural media-employed in radio transmission or a conductive transA mission line of any kind. A

Call signaling systems of this general type are known wherein the removal of the carrier wave from the transmission medium acuates a signa-ling device at the called station. Such systems may be defective however in the fact that any accidental removal of the carrier wave from the medium will cause the actuation of the signaling device and so give rise to a false signal indication.

The object of this invention isto provide an organization of elements in a system of this general ty e, wherein such defect will be overcome.. nother object of the invention is to provide acall signaling system wherein the signaling device will be actuated only when the carrier is removed from the transmission medium in a predetermined manner. Still another object is to provide a system of this kind which is not affected by foreign currents which may find their way into the system. A still further object is to provide a system which will accomplish the above results and still be simple in construction and operation.

These objects are` accomplished in the present invention, by providing means for removing the carrier wave from the transmission medium periodically at a4 predetermined rate and means at the called station for acutating a signaling device only in response to such removal at such predetermined rate. At a carrierwa've transmitting station a relay may be actuated in response to ordinary low frequency ringing current incoming from a calling station to intermittently short-circuit the carrier wave supply to a transmission line. At a cooperatin" receiving station a second relay may be actuated at each interruption of the carrier wave. A third relay controlled thereby and responsive only to such eriodic actuation may cause a signal indication at a called station.

Proceeding now to a detailed description of the invention with reference to the accom panyin drawing2 Fig. 1 shows one embodiment. t ereof. F 1g. 2 shows a detail of the system of Fig. 1. It is to be understood that other organizations of elements may be employed in the working of the invention.

Tn Fig. 1 there is shown, a two-way channel l of a carrier wave terminal station with its accompanying signaling apparatus and low frequency terminal line 3, and a second low frequency line 2 connected through suit-able means to a common transmission line ML. For the purpose of description one terminal station only of the system is shown. It is to be understood .that a similar cooperating station is connected to the distant end of the common line ML.

The low frequency line 2, terminating at one end in a station B is connected to the common line ML through a low-pass lter,

LP. This filter is of a type described in patent No. 1,227,113 issued on May 22, 1917 to G. A. Campbell. It will be referred to hereinafter as a low-pass filter since it is designed to pass without appreciable attenuation currents of all frequencies below and including the highest essential frequency of the voice range, and practically to extinguish currents of higher frequencies.

A carrier current terminal station is also connected to the common line ML through a high-pass filter HP. This filter is also of a type described in the Campbell patent mentioned above and hereina ter will be spoken of as a high-pass filter, since it is designed to pass without appreciable attenuation all currents having frequencies higher than the highest essential frequency of the voice range, and to suppress all currents of frequencies within the essential voice rang and below.

Connected to the two-way channcd 1 of the carrier terminal station is a low frequency line 3 terminating at the distant end in a low frequency station A.

Low reguency stations A and B, may be subscribers stations or, as is more common, they may be ordinary telephone exchanges. The station A, furthermore, may be located in the same building with the carrier apparatus or it may be located at a distance therefrom.

The low frequency line 3, at the carrier terminal station 1, extends through the normally closed contacts of relay l, the function of which will be described hereinafter, to the line terminals of a balanced transformer 5. A low frequency network LFN, connected to the opposite terminals of the balanced transformer 5 is provided to balance the low frequency line 3 in a welllrnown manner. rllhe series winding of the hybrid coil 5 is connected to the voice frequency input circuit of a modulator M. An oscillator C is also connected to the carrier current input circuit of the modulator M. The output circuit of modulator M is connected to a band lilter MBE. rlhis filter is adapted to pass a broad band of frequencies without substantial attenuation, while practically suppressing all frequencies outside of such band both above and below. This filter is also of the general type described in the Campbell patent mentioned above. Connected in series with the band filter MBP, are band filters MB1r2 and MB1"8 and one winding of transformer 6. rllhe other Winding of transformer 6 is connected across the bridge terminals of a high frequency balanced transformer 7. The line terminals of this coil are connected to the common line ML through the high pass filter lill?. Connected to the opposite terminals is a high frequency balancing network HFN. The circuit just described as extending between the balanced transformer 5 and the high frequency balanced transformer 7, comprises the transmitting channel 8 of the two-way carrier channel 1.

A corresponding receiving channel 9 of the two-way channel 1 comprises the series winding of the balanced transformer 7, detector band filter DBP connected in series with band lilters DBF2 and DBlFS, a voice frequency detector D, a receiving amplifier BA and a low pass filter LPF. This filter is similar to the low pass filter LP connected in the low frequency line 2.

The apparatus just described is used primarily for speech transmission. For signalingpurposes, an alternating current relay 10 is 'connected through a condenser 1l and normally closed lower armature and Macnee contact of relay 13 across the low frequency line 3 at a point between thenormally closed contacts of relay d and the balanced transformer 5. By means of this relay l0 the output circuit 'of the oscillator. O may be short-circuited for purposes hereinafter to be described. The slow release relay 13 is provided to guard the system against false operation. lts normally open upper contact controls a short circuit across the low frequency modulator input circuit, while its normally closed lower contact controls the continuity ofthe energizing circuit of relay 10.

Connected to the receiving circuit 9 between the receivinxg amplifier RA and the low pass filter LP and in shunt therewith is a signal detecting circuit. rl`his circuit comprises a high pass lilter HPF, a singal detector SD, a relay 14, a condenser 15 and a battery 16. The high pass filter HPF may be of the same type as the high pass filter Hl). The signal detector SD may be of the well-known three electrode thermionic vacuum tube type, which is adapted to translate alternating current of carrier wave frequency into uni-directional current for the operation of relay 14. The battery 16 provides the energy for the operation of relay 11, while the condenser 15 is connected across the windings of relay 1/1 to improve the operation in a well-known manner. Relay 14 controls the energizing circuit of a relay 17. lin either the actuated or 11n-actuated position of relay 1l a circuit is closed from ground to ground through a battery 18, the winding of relay 17 and one or the other of the contacts ot relay 14.

Relay llt is a two-position relay. The

term twoposition relay7 as used in this specification means a relay having at least two contact closures whereby two identical or equivalent circuits may be completed therethrough under different energization conditions of the relay. For example, the energizing circuit of relay 17 is closed by the closure of either the front or back contacts of relay 14, therefore. relay 14 is termed a two-position relay.

Relay 17 through its normally open contactcontrols a signal lamp 19, the signaling relay el, and the guarding relay 13. Lamp 19, relay 4land relay 13 are energized by current from batteries 20, 21, and 22 respectively.

Relay 4 controls the application of ringing current to the low frequency line 3 through its normally open front contacts from the source of ringing current 23.

A. thermionic discharge device suitable for use as a signal detector is shown in Fig. 2. The lettered terminals of the arrangement of Fig. 2 are connected to the correspondingly lettered terminals of Fig. 1. The device of llig. 2 operates in well-known manlll? ner, but for further description reference ma be had to an article by Messrs. Colpitts an Blackwell on Carrier currenttelephony and telegraphy published in the Journal of the American Institute of Electrical Engineers for April, May and June 1921.

'I he operation of" the system for call signaling will now be described.

Let it be assumed that a party at station A desires to get the attention of a party at a cooperatin station at the distant end of the common line ML. By the usual ringing ap aratus at such a station, ringing current wi l be impressed upon line 3 and, flowing through vthe normally closed contacts of relay 4, normally closed contact of relay 13, winding of relay 10 and the condenser 11,

.will actuate relay 10 periodically at a rate determined by the frequency of the ringing n circuit. Such operation of relay 10 will intermittently short-circuit the output of the oscillator O by intermittently closing a shortcircuit at the normally open contact of relay 10. The effect of this will be to intermittently remove the carrier Waves at the same rate from the common line ML. It is, of course, understood that carrier waves of distinctive frequency are normally impressed upon the common line ML through the modulator M, the transmitting modulator band filter MBF1,.-the end-sections of modulator band filters MBF2 and MBPS, the transformer 6, the balanced transformer 7, and the high pass filter HP.

Referring now to receiving channel 9 which for purposes of description will be considered as the cooperating distant station, the normally transmitted carrier waves will be normally received from the common line ML through the high pass filter HP, the balanced transformer 7, the end sections of detector band filters DBF3 and DBF2, detector band filter DBF 1, detector D, receiving amplifier RA, and high pass filter HPF, by the signal detector SD. The high frequency carrier wave is translated by the signal detector SDainto uni-directional current, to cause the actuation of relay 14. The interruption of the carrier wave at the transmitting station by interrupting the fiow of energy to the winding of relay 14 allows its armature to retract against its back Contact. Relay 17 is so designed that a single change of position of the armature of relay 14 will not permit sufficient deenergization .of relay 17 to allow its armature to retract. On the other hand, the d6- sign of relay 17 is such that when the armature of relay 14 vibrates between its front and back contacts at a rate corresponding to the intermittent interruption of the carrier wave at the transmitting station, relay 17 will be deenergized. In order now to again energize relay 17, the armature relay 14 must remain quiescent in either its actuated 'or unactuated position for a relatively long period of time. In other Words, relay 17n`s relatively' quick to release but slow to operate.

lVhen rela 17 releases, its normally open contact is clbsed, signal lamp 19 being lighted and relays 4 and 13 being energized v thereby. The circuit for lamp 19 extends from ground, through 'battery 20, lamp 19, closed contact of. relay 17 to the ground side of battery 18. The energizing circuit ofrelay 4 extends from ground, through battery 21, winding of relay 4, closed contact of relay 17, to the ground side of battery 18. Theenergizing circuit of'relay 13 extends from ground, through battery 22, winding of relay 13, closed contact of relay 17, an the ground side of battery 18.

The lighting of lamp 19 provides a signal at the carrier terminal station to indicate that the distantcooperating station is calling. Relay 13 which is quick to operate opens the energizing circuit of relay 10 at its own normally closed lower back contact (now open) and so prevents thc party at station A from originating a call. At the same time, the operation of relay 13 short circuits the low frequency input circuit of the modulator M at its normally open upper front contact (now closed). Relay 13 is designed to operate quickly in order that these functions may be performedbefore the slow-operating relay 4 has caused ringing current from the source 23 to be impressed upon line 3 through its front contacts (now closed). It is necessary to shortcircuit the low frequency input circuit of modulator M at this time to prevent singing, since the'normally balanced transformer 5 becomes unbalanced when the low frequency line 3 is removed by the operation of relay 4. The impression of ringing current on the line 3 from the source 23 op erates a signaling device at station A to attract the attention of the called party.

It should be noted that the same carrier frequency is employed by the calling station for transmission, as is used by the cooperating receiving station for reception. It should be further noted that carrier waves of distinctive frequencies are used at each twoway channel for transmissions in opposite directions and that carrier waves of distinctive frequencies are used for transmission through the several channels of the same station. In some cases the distinctive frequencies of the carrier waves used .for transmission by the several channels may be grouped together in a continuous frequency range and the distinctive frequencies used for reception may likewise be grouped together though in a different continuous frequency range. In other cases the distinctive frequencies used for transmission may alternate with the distinctive frequencies used for reception' and may extend over the whole frequency range.

In the drawing, the complete circuit of one channel only is shown While two additional channels are merely indicated. lt is to be understood that the system is not to be limited to any particular number of channels but that any number of additional channels may be added as the requirements of the case may demand.

l't is, of course, understood that the invention is not limited by this particular arrangementof elements but is to be limited only by the scope of the appended claims.

What is claimed is:

1. A method of signaling in a carrier wave si aling system employing 'a two-position re ay, a controlled element and a second relay for controlling said element, which method comprises receiving impulses of carrier waves at a predetermined impulse periodicity, actuating the controlled element only when the two-positioned relay is changing from one position to the other and vice versa at a predetermined rate, andenergizing the Y second relay to prevent actuation of the controlled element when the first relay remains in either position for a duration of time exceeding a definite minimum period.

2. ln a signaling system, a transmission medium` means to impress carrier waves on said medium, means to periodically withdraw said waves from said medium at a predetermined rate, a two-positioned relay maintained in one of its positions by the incoming carrier wave and in the other position when the carrier wave is withdrawn, a second relay energized when said first mentioned relay remains in either of its two positions during a period of time longer than that due to the predetermined rate of withdrawal of the carrier waves, and a signaling device controlled by said second relay.

3. ln a signaling system, a transmission medium, means to impress carrier waves on said medium, means to periodically withdraw said waves from said medium at a predetermined rate, atWo-position relay maintained in one of its positions by the incoming carrier wave and in the other position when the carrier wave is withdrawn, a second relay energized when said first mentioned relay remains in either oi. its two positions during a period of time longer than that due to the predetermined rate of Withdrawal of the carrier waves, and deenergized when said first mentioned relay is alternating between its two positions in synchronism with the withdrawal of the carrier wave and a signaling device controlled by said second relay.

4. A call signal receiving system comprising a therminonic device adapted to translate high frequency oscillations into unidiinsonne rectional current, a relay connected to said thermionic device and adapted to be normallyl energized by unidirectional current therefrom, a second relay, an energizing lcircuit 'or said second relay, the continuity of which is completed by said rst mentioned relay when in either its energized or deenergized condition and interrupted during the period of change from the energized to the deenergized condition and vice versa, and a signaling device controlled by said second mentioned relay.

5. A call signal receivingsystem comprising a thermionic device adapted to translate high frequency oscillations into unidirectional current, a relay connected to said thermionic device and adapted to be normally energized by unidirectional current therefrom but responding to interruptions 'of said oscillations at a predetermined rate to change the position of its armature, a second relay, an energizing circuit for said second relay the continuity of which is interrupted b the response of said first men tioned re ay to the interruption of said oscillations at said predetermined rate and a si al controlled by said second mentioned re ay.

6. ln a call signaling system, a transmission medium, means to impress a carrier wave on said medium, means to periodically withdraw said Wave from said medium at a predetermined rate, a receiving station, a signal at said receiving station, a two posi- 'tion relayf maintained in one position by the received carrier wave and in the other when the carrier wave is withdrawn, a second relay adapted to cause an indication by said signal when said first mentioned relay is changing position at the predetermined rate of interruption of said carrier wave and to prevent such indication when said iirst mentioned relay remains in either of its positions longer than a predeterminable period corresponding to said predetermined rate.

7. ln a carrier Wave call signaling system, a plurality oi speech transmlssion channels, carrier waves of distinctive frequencies normally impressed upon each channel, means to intermittently withdraw any of said waves from their corresponding channels at a predetermined rate, a two-position relay for each channel, each of said relays being maintained in one of its positions by the carrier wave of distinctive frequency assigned to that channel and in the other posi'- tion when said carrier wave is withdrawn, a second relay for each channel energized when said first mentioned relay remains in either of its two positions during a period of time longer than that due to the predetermined rate of withdrawal of the carrier waves, and a'signaling device for each channel controlled by said second relay.

8. lin a carrier wave call signaling system,

a plurality of speech transmission channels, carrier Waves of distinctive frequencies normally impressed upon each channel, means to intermittently Withdraw any of said Waves from their corresponding channels at a predetermined rate, a two-position relay for each channel, each maintained in one of its positions by the carrier Wave of distinctive frequency assigned to that channel and in the other position when said carrier Wave is Withdrawn, a second relay, means to energize said second relay when said first mentioned relay is changing its position in synchronism with the withdrawal of the carrier Wave and a signaling device controlled by said second relay.

9. A signaling system comprising a line,

means for applyinr periodic impulses of al ternating current. `thereto, a relay responsive to said impulses, a controlled element, and a slow-operating quick-releasing relay controlled by the rst relay and controlling said element.

10. A signaling system comprising a transmission medium, means for impressing periodic impulses of alternating current thereon,

a relay responsive to said impulses, a controlled element, and a slow-operating quickreleasing relay controlled by the first relay and controlling said element.

In Witness whereof, I hereunto subscribe my name this 17th day of December, A. D.,

CHARLES WHITE. 

